Couplers are generally components that have four accesses or ports, i.e. two inputs and two outputs, where a signal applied to one of the inputs has its power halved and reproduced at both outputs, with the non-fed input being isolated. At the two outputs, the vectors representing complex voltages are orthogonal, i.e. the complex voltages (which have the same amplitude) have a phase relationship that is either in quadrature or else in phase opposition.
In numerous applications, for example such as the multiple beam forming arrays of antennas or amplifiers having multiple ports, it is desirable to have hybrid couplers which, while conserving the above properties of isolation between inputs and of complex voltage vectors at their outputs that are orthogonal, nevertheless possess more than two inputs and two outputs.
Butler matrices and so-called "generalized" couplers are examples of such multipleport couplers.
Such multiple port couplers are generally constituted by elementary four-port hybrid couplers that are combined together by transmission lines. The principles on which they are based means that their numbers of inputs and outputs are always powers of two, and they also include transmission lines that cross over one another, thereby complicating manufacture.
To enlarge the range of possible combinations, it would be desirable to have compact couplers with three inputs and three outputs, the inputs being matched and isolated, and with each of the inputs being capable of delivering a uniform distribution of power to the three outputs, with the power distribution from each input being orthogonal to the distribution from the other two inputs.
Such components would make it possible to extend the structure of generalized couplers by greatly simplifying the implementation of matrices having a number of inputs or of outputs that is a multiple of three, for example 3.times.3, 6.times.6, or 9.times.9, etc. square matrices, or 3.times.6, 6.times.3, 3.times.9, etc. rectangular matrices.
The object of the present invention is to provide such a microwave coupler having three isolated and matched inputs each producing a distribution at the three outputs that is uniform in amplitude and orthogonal to the distributions corresponding to the other two inputs, and also to provide generalized couplers making use of such elementary 3.times.3 couplers.
The only 3.times.3 coupler having these properties that has been proposed in the literature is a component described in an article by J. P. Shelton and K. S. Kelleher, entitled "Multiple beams from linear arrays", published in IRE Transactions on Antennas and propagation, March 1961, pp. 154-161, and in particular Appendix I, pp. 158-160, entitled "Six-port junction for multiple-feed arrays".
That coupler, which is shown diagrammatically in FIG. 1, has three inputs 1, 3, and 5, and three outputs 2, 4, and 6 interconnected essentially by components referenced 20, namely three transmission lines 21 disposed symmetrically and interconnected transversely by two series of crossmembers 22 and 23; in the zone lying between the components 21, 22, and 23, this configuration establishes square coupling regions that distribute power between the three lines 21. To ensure that the phases of the signals at the three outputs 2, 4, and 6 are at mutual uniform phase differences of 120.degree. , a phase shifter circuit 24 is inserted in one of the lines. This circuit 24 which adds a phase shift of 120.degree. thus makes it possible to obtain the looked-for phase relationship between the outputs.
This type of coupler has hardly been used in practice, and it suffers from several drawbacks, in particular excessive bulk, and manufacturing difficulties because of the difficulties in dimensioning the various components (on which topic the above-mentioned article is silent), with a correspondingly high cost.
In addition, because of its threedimensional configuration, such a coupler necessitates the use of coaxial line technology or waveguide technology, thereby limiting the situations in which it can be used, or else requiring interfacing with transmission lines made using some other technology, thereby increasing difficulties in implementation and in development.
The present invention seeks to remedy these drawbacks by providing a 3.times.3 coupler of the above-specified type but made using a configuration that is essentially plane, thus lending itself to being implemented using a wide variety of technologies such as microstrip, stripline, square coaxial line, called "bar line", etc.